Macaulay2 / Macaulay2/M2

incorrect cohomological shift for modules

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package issue
Dominant language
Macaulay2
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Merged PRs (30d)
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Description

```m2
i1 : needsPackage "Complexes";

i2 : S = QQ[x];

i3 : S^1[1]

1
o3 = S

1

o3 : Complex

i4 : (complex S^1)[1]

1
o4 = S

-1

o4 : Complex
```

cc: @mikestillman @ggsmith

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the `Complexes` package examples in the issue, especially `S^1[1]` and `(complex S^1)[1]`. Trace how the package represents and applies cohomological shifts, then verify that both expressions produce the intended degree convention and add or update a regression test if the relevant test location can be found.

Written by the indexing model from the issue text.

Assessment

Domain
tooling
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
45/100

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